The study will examine the metabolism of exogenous fatty acids by Macaca fascicularis. Trans fatty acids which can not be synthesized by eukaryotes will be used as the exogenous fatty acid marker. Trans fatty acids are geometrical isomers of cis-fatty acids which can be synthesized by eukaryotes. Trans fatty acids are not toxic as long as the essential fatty acid requirements are satisfied. The trans fatty acids are catabolize and removed from the body shortly after they are removed from the diet. Twelve male Macaca fascicularis monkeys will be used in the study. Six of the monkeys will be fed the control diet and the others will be fed the experimental diet containing trans fatty acids. Thirty-six weeks will be required to complete the study. The objectives of the study are to: 1) Determine if the monkeys have the gut flora required to produce trans fatty acids. 2) Determine if trans fatty acids are incorporated into the RBC membrane of the monkeys. 3) Determine if the trans fatty acids incorporated into the RBC membrane effect the membrane function by examining a membrane-bound enzyme.